hardly be supposed that a false theory would explain, in so
satisfactory a manner as does the theory of natural selection, the
several large classes of facts above specified. It has recently been
objected that this is an unsafe method of arguing; but it is a method
used in judging the common events of life, and has often been used by
the greatest natural philosophers. The undulatory theory of light has
thus been arrived at; and the belief in the revolution of the earth on
its own axis was until lately supported by hardly any direct evidence.
It is no valid objection that science as yet throws no light on the far
higher problems of the essence of the origin of life. Who can explain
what is the essence of the attraction of gravity? No one now objects to
following out the results consequent on this unknown element of
attraction; notwithstanding that Leibnitz formerly accused Newton of
introducing "occult qualities and miracles into philosophy."

I see no good reasons why the views given in this volume should shock
the religious feelings of any one. It is satisfactory, as showing how
transient such impressions are, to remember that the greatest discovery
ever made by man, namely, the law of the attraction of gravity, was also
attacked by Leibnitz, "as subversive of natural, and inferentially of
revealed religion." A celebrated author and divine has written to me
that "he has gradually learned to see that it is just as noble a
conception of the Deity to believe that He created a few original forms
capable of self-development into other and needful forms, as to believe
that He required a fresh act of creation to supply the voids caused by
the action of His laws."

Why, it may be asked, until recently did nearly all the most eminent
living naturalists and geologists disbelieve in the mutability of
species? It cannot be asserted that organic beings in a state of nature
are subject to no variation; it cannot be proved that the amount of
variation in the course of long ages is a limited quantity; no clear
distinction has been, or can be, drawn between species and well-marked
varieties. It cannot be maintained that species when intercrossed are
invariably sterile and varieties invariably fertile; or that sterility
is a special endowment and sign of creation. The belief that species
were immutable productions was almost unavoidable as long as the
history of the world was thought to be of short duration; and now that
we have acqui